Silicon carbide has many useful features not found in various other semiconductor materials. In particular, its refractory nature, inertness, and high energy gap allow high power dissipation and superior reliability. It has several crystalline forms including the cubic or beta form.
The economic fabrication of various semiconductor elements requires the use of relatively large and homogeneous SiC monocrystals otherwise known as single crystals. They make use of both vapor phase (including chemical vapor) deposition and liquid phase deposition. The art teaches the use of molten silicon as a solvent for liquid-phase deposition of SiC single crystals, but unfortunately the solubility of SiC in silicon is quite low at any temperature that might heretofore have been considered reasonable, e.g., less than 2000.degree. C.
Heretofore at least, a preferred solvent has been chromium, although the rare earths have also been used. Thus, for example, U.S. Pat. Nos. 2,996,456 and 3,278,274 teach the use of chromium as a solvent in the growth of SiC single crystals. The temperature required in both instances is said to be 1700.degree. C. or higher. There is no indication in either patent as to what form of SiC is produced.
More recently, alloys or compounds of the transition metals and silicon have been used as solvents for the liquid-phase production of SiC single crystals. Using Ti-Si alloys, the growth temperature is in the range of 1600.degree. to 1700.degree. C. See P. W. Pellegrini and J. M. Feldman, "LPE Growth of SiC Using Transition Metal-Silicon Solvents," in Silicon Carbide--1973 edited by Marshall et al., pp. 161-167 (University of South Carolina Press, Columbia, S.C. 1974).
The cost of production of SiC single crystals can be materially reduced if the temperature at which the single crystals are formed can be lowered substantially. This also permits the use of a greater variety of crucible materials.
Accordingly, it is an object of this invention to provide a method for the liquid-phase growth of SiC single crystals.
It is another object of this invention to provide a method for the liquid-phase growth of SiC single crystals at a temperature substantially less than 1600.degree. C.
A further object of the invention is to provide a method for the liquid-phase growth of beta SiC single crystals using a novel metal solvent.